This invention concerns a process for making certain thienopyridine and furopyridine 2-anionic salts.
Thienopyridines and furopyridines bearing no substituents are well known. Substituted thieno (furo)-pyridines are less well known because of the difficulty of synthesis. Maffrand and Boigegrain recently have disclosed a synthesis of certain 2-substituted thieno[3,2-c]pyridines by thermal rearrangement of thienyl oxazolidines; Heterocycles Vol. 12, No. 11, 1479 (1979). Direct electrophilic substitution of unsubstituted thieno(furo)pyridines has not afforded 2-substituted thieno(furo)pyridines, presumably due to the relative unreactivity of the 2-position. Indeed, both thieno[3,2c] and thieno [2,3c]pyridines have been shown not to react at the 2-position with strong bases such as n-butyl lithium to form the 2-anion; see Advances in Heterocyclic Chemistry, 21, 96 1977. Dressler and Joullie reported that electrophilic attack occurred only at the 3-position in all of the thienopyridines that were studied; J. Heterocyclic Chemistry, 7, 1257 (1970).
An object of this invention is to provide a convenient process for preparing thieno(furo)pyridine 2-anionic salts from the corresponding 2-unsubstituted thieno(furo)pyridines by reacting a thieno(furo)pyridine with a non-nucleophilic alkali metal base.